You read that right. This is the step you should take even before you take your first step. What I mean is conceptualization.
Concept is the leading force behind both design and development. When it comes to maps, it is even more important. Maps are more than just a pretty place to have a gunfight, or to fight monsters. It has to be balanced, so that the player or players can’t simply climb up a ledge and be unreachable from the other players. It also has to be well kept, so the player isn’t getting stuck in the gaps between your two decorative rocks.